This application is based on and incorporates by reference Japanese Patent Application No. 2001-54486 filed on Feb. 28, 2001.
1. Field of the Invention
Embodiment of the present invention relate to a high pressure fuel pump used for a gasoline engine and a diesel engine in which fuel is directly injected into a cylinder and is burned. In particular, at least one embodiment of the invention relates to a high pressure fuel pump provided with a flow amount control valve capable of controlling the flow amount of a high pressure fuel supplied to a delivery pipe such as a common rail (high pressure accumulation pipe), or the like.
2. Description of the Related Art
In recent years, gasoline and diesel engines are required to satisfy not only high power, low noise, and low fuel consumption requirements but also rigorous emission regulations. In order to meet these requirements, attention has been paid to a direct injection type gasoline engine and a direct injection type diesel engine in which the injection timing and the injection amount of the fuel are controlled with high accuracy. Usually in these engines, the fuel is drawn from a fuel tank by a low pressure fuel pump and is further pressurized by a high pressure fuel pump and supplied to a delivery pipe such as a common rail or the like and is directly injected into cylinders through injectors connected to the delivery pipe.
In order to control the injection timing and the injection amount of the fuel with high accuracy, the injectors and the high pressure fuel pump are electronically controlled. Such a high pressure fuel pump electronically controls the fuel supply amount to the delivery pipe according to the injection amount of the injectors. This is unlike a fuel injection pump in the related art for controlling the flow amount of the fuel by adjusting the positional relationship between a reed provided on a plunger and an intake/exhaust port. To be more specific, by controlling the timing of overflowing the fuel in a pump chamber to a low pressure side, the supply amount of the fuel compressed and discharged to the delivery pipe by the plunger is adjusted to keep a fuel pressure in the delivery pipe at a predetermined pressure.
Here, as to the flow amount control valve which is important in controlling the flow amount of the high pressure fuel pump, various propositions have been made and among them, a pilot type flow amount control valve capable of reducing cost is disclosed in JP-A No. 8-49617 and JP-A No. 2000-186649.
A solenoid spill valve 20 disclosed in the JP-A No. 8-49617 is a pilot type inwardly opening (solenoid) valve comprising a needle valve 4 for opening/closing a seat plane 12 provided in the overflow passage of the fuel and a moving member 6 for driving the needle valve 4. Here, the numerals in the parentheses denote the reference numerals shown in FIG. 1 in the official gazette. In the solenoid spill valve 20, a fuel inlet passage 11, which is to be an overflow passage, is made to communicate with a hydraulic chamber 8 provided on the back of the needle valve 4 by a slim pressure introduction passage 16. However, since the moving member 6 moves in the hydraulic chamber 8 of a small volume, a pressure pulsation is caused and is propagated through the pressure introduction passage 16 with a time lag and causes variations in the response of the needle valve 4. Further, the pressure introduction passage 16 is provided with an orifice 14. In order to eliminate the pressure pulsation causing the variations in the response of the needle valve 4, the diameter of the orifice 14 needs to be made considerably small, or conversely, the diameter of the pressure introduction passage 16 needs to be made considerably large, which is not realistic in either case because of manufacturing costs.
The high pressure fuel pump 1 disclosed in JP-A No. 2000-186649 has a pilot type outwardly opening (solenoid) valve comprising an intake valve 30 for opening/closing a valve seat 34 provided in the fuel overflow passage and a control valve 50 for driving the intake valve 30. Here, the numerals in the parentheses denote the reference numerals shown in FIG. 2 in the official gazette. In the control valve 50, the fuel in a control chamber 45 provided on the head 48 of the intake valve 30 flows in or out to temporarily make the control chamber 45 a rigid body thereby controlling the opening/closing of the valve seat 34 by the intake valve 30. Also in this case, since the volume of the control chamber 45 is small, the volume of the control chamber 45 fluctuates substantially by the operation of the control valve 50, and a large pressure pulsation caused by the fluctuation of the volume of the control chamber 45 is propagated to a fuel well 24 through a communication passage 46. It is then propagated to a pump chamber 16 in which the valve seat 34 is arranged through an insertion hole 35 to cause variations in the response of the intake valve 30, which might cause the deterioration of controllability.
Here, as to a valve structure, a xe2x80x9cpilot type valvexe2x80x9d means a valve part abutting against a valve seat surface is separated from a driving part, and an xe2x80x9cinwardly opening valvexe2x80x9d means a valve in which the seat surface of a port is disposed on the driving part side (inside) and in which the valve part is opened inwardly. The xe2x80x9coutwardly opening valvexe2x80x9d means a valve in which the seat surface of a port is disposed on the side opposite to the driving part (outside) and which the valve part is opened outwardly. These descriptions are used throughout the specification and are meant to have the same meaning.
The present invention has been made in view of these circumstances. It is an object of at least one embodiment of the present invention to provide a high pressure fuel pump having a flow amount control valve of excellent controllability which can suppress the effect of a pressure pulsation caused by the operation of a driving part (moving member) and whose valve shows stable response.
Thus, the present inventor has conducted research to solve the problem described above, and has discovered an idea for making a flow amount control valve of a pilot valve type, that is, an outwardly opening valve. Additionally discovered is a way of increasing the rate of the total volume of an operating chamber, in which the moving member is disposed, to accommodate the variable volume thereof, and thus has achieved a high pressure fuel pump of the present invention.
That is, a high pressure fuel pump in accordance with an embodiment of the present invention is characterized as a high pressure fuel pump including a pump body having a pump chamber formed in such a way as to communicate with a low pressure fuel passage connected to the supply source of a low pressure fuel and a high pressure fuel passage for supplying a high pressure fuel to an injector side. Additionally, a plunger is fitted into the pump chamber and supplied with a driving force from a driving source to slidably move back and forth in the pump chamber thereby to draw and discharge fuel. Also provided is a flow amount control valve for adjusting the flow amount of the high pressure fuel to the high pressure fuel passage by opening or closing a spill port provided in the overflow passage of the fuel which communicates with the pump chamber. The flow amount control valve has a valve body having an operating chamber which is formed on the side opposite to the pump chamber with respect to the spill port and communicates with the overflow passage. A valve part exists which is urged in the direction that seats the valve part on a valve seat formed on the pump chamber side of the spill port and which is separated from or seated on the valve seat to open or close the spill port. Furthermore, there is a moving part which is separated from the valve part and disposed in the operating chamber and electromagnetically controls the opening or closing of the spill port by the valve part. Finally, a stem part is provided which is disposed in the operating chamber and transmits an urging force from the moving part to the valve part, the urging force being applied by the moving part to the valve part in the direction that separates the valve part from the valve seat, and which is more slender than the moving part. Since the flow amount control valve is a pilot type outwardly opening valve in which the valve part is separated from the moving part, it is possible to improve the response of the valve part and it is not necessary to make the respective parts with high machining accuracy, for example, in concentricity or the like, which makes it possible to manufacture the flow amount control valve at a comparatively low cost.
In addition, in the flow amount control valve in accordance with an embodiment of the present invention, the slender stem part disposed in the operating chamber is interposed between the moving part and the valve part and the switching of the urging force applied to the valve part by the stem part makes it possible to surely open or close the spill port. Therefore, since the stem part is more slender than the moving part, the volume (V) formed in the operating chamber is made larger. Then, even if the moving part is moved in the operating chamber to produce a change in volume (xcex94V), the rate of change in volume (xcex94V/V) is relatively small in terms of the whole operating chamber and thus a fluctuation in pressure (pressure pulsation) caused by the movement of the moving part becomes small. Therefore, the variations in the response of the valve part, which is caused by the pressure pulsation, is reduced to improve the controllability of the flow amount control valve.
In this connection, it is essential only that the degree of xe2x80x9cslendernessxe2x80x9d of the stem part provide the stem part with the rigidity necessary for the stem part to function as the stem part. There is no restraint on size or shape. For example, in the case where a moving part having a large diameter is fitted in a cylindrical operating chamber, it is acceptable that the stem part is formed in the shape of a column having a diameter smaller than the moving part. Further, the operating chamber is formed in various shapes, for example, the volume (V) of the operating chamber may be partially expanded.
Still further, although it is necessary that the moving part be separated from the valve part, it is not necessary that the stem part be separated from the moving part and the valve part. For example, the stem part may be integral with the moving part and the stem part may be integral with the valve part. Of course, it is possible to support the stem part with an appropriate guide part and to form them in a three-way structure.
Urging the valve part in the direction that seats the valve part on the valve seat or urging the valve part in the direction that separates the valve part from the valve seat by the moving part can be performed by an elastic member such as a coil spring or a coned disc spring. Although it is thought that such urging can be performed by an electromagnetic force, the urging by the use of the elastic member can reduce the cost and the size of the flow amount control valve. Then, for example, it is preferable that the foregoing moving part elastically urge the foregoing stem part in the direction which separates the valve part from the valve seat and that the elastic urging is released by the application of an electromagnetic force. In this respect, of course, in order to surely close the spill port without putting the valve part into contact with the stem part when the plunger pressurizes the fuel, the length of the stem part needs to be set in such a way that the displacement (L1) of the moving part is larger than the displacement of the valve part (L2) (L1 greater than L2).
It is preferable that the operating chamber constitute at least a part of a fuel well communicating with the low pressure fuel passage and that the spill port serves also as the intake port of the low pressure fuel to the pump chamber.
This can make the low pressure fuel passage simple and reduce the size of the high pressure fuel pump. Further, since the spill port serves also as the intake port, a force in accordance with the movement of the plunger is applied to the valve part disposed at the spill port to further improve the response of the valve part. For example, in the case where the plunger is in the intake stroke (i.e. a down-stroke), a negative pressure is applied to the plunger side of the valve part to move the valve part in the direction that opens the intake port. Conversely, in the case where the plunger is in the discharge stroke (an up-stroke), a positive pressure is applied to the plunger side of the valve part to move the valve part in the direction that closes the intake port. In this manner, both of the opening response and the closing response of the valve part can be improved.
Incidentally, the pump body may be separated from or integrated with the valve body. Further, the flow amount control valve varies the flow amount of the fuel so as to adjust the fuel pressure in the delivery pipe such as a common rail, and in addition, may adjust the timing of discharging the fuel. The engine employing the high pressure fuel pump in accordance with embodiments of the present invention is not limited to a direct injection type gasoline engine or a direct injection type diesel engine and is not limited to a common rail type engine, either. For example, in the case of the diesel engine, not only the direct injection type engine but also a swirl chamber type engine and a pre-combustion chamber type engine can employ this high pressure fuel pump. Further an in-line fuel injection pump or a distribution type fuel injection pump in the related art can be used as a high pressure, electronically controlled fuel pump.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.